The present invention relates to improvements in injection molding systems for molding molded articles, such as preforms.
Conventional preform molds, such as those shown in U.S. Pat. No. 4,432,530 to Marcinek, U.S. Pat. No. 4,634,366 to Brun et al., U.S. Pat. No. 5,470,221 to Gaiser, U.S. Pat. No. 5,498,150 to Check and U.S. Pat. No. 4,571,171 to Blank et al., teach a one piece cavity insert mating with a pair of neck ring inserts for forming the outer surface of the preform. These show the mating surface to be a conical taper that is used to align the components when the mold is closed and clamped by the injection molding machine. It is well known in the art, that such a mating taper, when used for alignment purposes, must be made of dissimilar materials so that disadvantageous galling and premature wear does not occur. Consequently, in conventional molds the cavity and neck ring inserts are usually made of different steels and/or are heat treated to different hardnesses and/or may be plated with different coatings. Naturally, this may be time consuming and expensive and may not be entirely effective. If both the cavity insert and the neck ring inserts were to be made of the same steel at the same hardness, such as stainless steel, galling of the tapers would occur leading to rapid wear and poor operation of the mold.
U.S. Pat. No. 5,232,718 to Miyazawa et al. shows a preform mold in which movable inserts are placed between the mold cavity insert and the neck ring inserts. The patent teaches that such a design is needed for molding a handle feature onto the preform, or to clear an undercut diameter on the body of the preform. There is no teaching of use of the same material at the same hardness, such as stainless steel, nor is there any teaching of what material the different components are made of. Indeed, conventional knowledge would teach that each part that has a mating tapered alignment surface with its neighbor must be made of a different material and/or be at a different hardness and/or have a different surface coating so that galling and premature wear is avoided.
Accordingly, it is a principal objective of the present invention to provide an injection molding system and method which avoids the foregoing difficulties.
It is a further object of the present invention to provide a system and method that enables the use of inserts of the same material at the same hardness, as for example, the cavity insert and neck ring inserts.
Further objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages are readily obtained.
The injection molding system of the present invention for molding molded articles comprises: a mold cavity for forming said molded articles, wherein said mold cavity is defined at least in part by a mold core defining inner walls of said molded articles, a first insert defining at least outer side walls of said molded articles, and a second insert defining an outer wall of a neck of the molded articles; a cavity plate at least partly surrounding said first insert; and a cavity flange retaining said first insert in said cavity plate.
The first insert is preferably a cavity insert, and including a gate insert adjacent the cavity insert defining an outer bottom wall of the molded article, wherein the cavity plate at least partly surrounds the gate insert and wherein the cavity flange retains said cavity insert and gate insert in the cavity plate. Advantageously, all elements that substantially define the mold cavity are stainless steel, and/or all elements that substantially define the mold cavity are metal elements which are heat treated to substantially the same hardness.
The present invention also provides a method for forming an injection molding system for molding molded articles, which comprises: forming a mold cavity for molding said molded articles and defining the mold cavity at least in part by a mold core defining inner walls of said molded articles, a first insert defining at least outer side walls of said molded articles, and a second insert defining an outer wall of a neck of the molded articles; at least partly surrounding the first insert by a cavity plate; and retaining the first insert in the cavity plate by a cavity flange.
Further features and advantages of the present invention will appear hereinbelow.